1. Field of the Invention
The present invention relates to a probe apparatus including such as an atomic force microscope (AFM) and a scanning tunneling microscope (STM).
2. Description of the Related Art
In recent years, a non-contact type atomic force microscope has rapidly advanced. This microscope vibrates a cantilever serving as a probe with self-excitation to detect a small shift of the resonance frequency caused due to a charge-transfer force between the cantilever and a sample, thereby enabling nanoscopic measurement of a surface electron state (see, e.g., U.S. Pat. No. 7,250,602). Since this microscope detects a frequency, the microscope has resistance to noise and can detect an fN (femto-Newton) level force since a frequency is detected. Therefore, a single atom as well as a small charged state that is not greater than a single charge can be readily detected.
However, observation of an image with respect to a photoexcited electron transfer process is required by measuring a change in an electron state in a short time (e.g., nanoseconds) in addition to nanoscopic measurement of a surface electron state. Here, detecting a fast signal is attempted in the STM. But, since local charges diffuse to a conductor substrate, a time resolution of the STM cannot be exploited. Further, in the AFM, a single charge on an insulator can be detected by an electrostatic force. But, a scanning time is longer than 10 seconds, and it is approximately 0.1 second even in a special high-speed AFM. Therefore, a dynamic process cannot be tracked.
In nature, a subtle stereoscopic nano-structure is configured, and it has been revealed that a nanoscopic spatial arrangement is decisively important in highly efficient photoexcited electron transfer that can be observed in photosynthesis. However, when analyzing these structures in a conventional technology, there is only an indirect method, such as comparing a kinetic study on a solution-based molecular population with a crystal structure analysis using an X-ray or radiation light.